1. Field of the Invention
The present invention relates to a mobile communication system. More particularly, the present invention relates to a method for controlling transmission/reception timings of physical channels in a Time Division Duplex (TDD) communication system supporting carrier aggregation, particularly when the cells operate in different TDD configurations.
2. Description of the Related Art
A substantial amount of research is being conducted on the Orthogonal Frequency Division Multiple Access (OFDMA) and Single Carrier-Frequency Division Multiple Access (SC-FDMA) in the cellular communication field. Such multiple access technology is used to allocate and manage time-frequency resources for data transmission and/or control information transmission to and from multiple users without overlapping from each other (i.e. orthogonally) so as to discriminate among the multiple users.
A significant feature of the cellular communication system is support for scalable bandwidth for providing high speed data service. For example, a Long Term Evolution (LTE) system can support various bandwidths (e.g., 20/15/5/3/1.4 Mhz). Meanwhile, a LTE-Advanced (LTE-A) system can support high data rate transmission over a wide bandwidth (e.g., up to 100 MHz) for a single UE using a Carrier Aggregation (CA) technique. Mobile carriers can provide their services by selecting one of the available bandwidths, and the User Equipment (UE) can operate with various capabilities of a minimum 1.4 MHz bandwidth up to 20 MHz bandwidth.
In order to support the high data rate transmission, the LTE-A system requires the bandwidth wider than that of the LTE system while preserving backward compatibility to the legacy systems for supporting the LTE UEs.
For the backward compatibility, the system bandwidth of the LTE-A system is divided into a plurality of subbands or Component Carriers (CCs) that can be used for transmission/reception of data with LTE UEs and aggregated for the high data rate transmission of the LTE-A system with the transmission/reception process of the legacy LTE system per Component Carrier.
Each Component Carrier or cell can be categorized into one of a primary cell and a secondary cell according to its usage or significance. From the view point of the UE, only one primary cell exists with other secondary cells. In such an LTE-A system, the uplink control channel can be transmitted in the primary cell while uplink data channel can be transmitted in both the primary and secondary cells.
Typically, the scheduling information for the data transmitted on the Component Carriers is transmitted to the UE in Downlink Control Information (DCI). The DCI can be configured in various formats. That is, the DCI is generated in a different DCI format according to whether scheduling information is of uplink or downlink, whether the DCI is compact DCI, whether spatial multiplexing with multiple antennas is applied, and whether the DCI is the power control DCI. For example, the DCI format 1 for the control information about downlink data to which Multiple Input Multiple Output (MIMO) is not applied includes the following control information.                Resource allocation type 0/1 flag: The resource allocation type 0/1 flag notifies the UE of whether the resource allocation type is type 0 or type 1. Type 0 indicates resource allocation in a unit of Resource Block Group (RBG) in a bitmap method. In LTE and LTE-A systems, the basic scheduling unit is Resource Block (RB) representing a time resource and a frequency resource. An RBG includes a plurality of RBs and basic scheduling unit of type 0. Type 1 indicates allocation of a specific RB in RBG.        Resource block assignment: The resource block assignment information notifies the UE of an RB allocated for data transmission. At this time, the resource expressed according to the system bandwidth and resource allocation scheme is determined.        Modulation and coding scheme: The modulation and coding scheme notifies the UE of a modulation scheme and a coding rate applied for data transmission.        Hybrid Automatic Repeat reQuest (HARQ) process number: The HARQ process number information notifies the UE of a HARQ process number.        New data indicator: The new data indicator notifies the UE of whether the transmission is HARQ an initial transmission or a retransmission.        Redundancy version: The redundancy version information notifies the UE of a redundancy version of HARQ.        
Transmit Power Control (TPC) command for Physical Uplink Control Channel (PUCCH): The TPC command for PUCCH notifies the UE of power a control command for a PUCCH as an uplink control channel.
The DCI for notifying the UE of these information elements is transmitted on the Physical Downlink Control Channel (PDCCH) through channel coding and modulation process.
FIG. 1 is a diagram illustrating a physical control channel allocation method according to the related art. That is, FIG. 1 an example in which the Evolved Node B (eNB) schedules downlink data for the UE in an LTE a system operating with two aggregated Component Carriers (i.e., CC#1 and CC#2).
Referring to FIG. 1, the eNB applies a DCI format defined in the legacy LTE to the DCI 101 transmitted on the Component Carrier #1 (CC#1) 109 and performs channel coding and interleaving 103 to generate a PDCCH 105 as a control information channel. Next, the eNB notifies the UE of the scheduling information about a Physical Downlink Shared Channel (PDSCH) 107 as data channel allocated to the UE on the CC#1 109.
The eNB applies a format defined in the legacy LTE to the DCI 111 transmitted on the Component Carrier #2 (CC#2) 119 and generates a PDCCH 115 as a control information channel. Next, the eNB notifies the UE of the scheduling information about PDSCH 117 as data channel allocated to the UE. The eNB may perform channel coding and interleaving 113 to generate the PDCCH 115 as the control information channel.
In case of applying the timing relationship among the physical channels transmitting a PDSCH and an UL Acknowledgement/Negative Acknowledgement (ACK/NACK) of an LTE TDD system to an LTE-A system supporting carrier aggregation, no addition operation is necessary to be defined except for the related timing relationship. Because LTE-A specifies that the UL control channel is transmitted only in the primary cell, if the cells are configured with different TDD UL-DL configurations, it is necessary to define the time relationship of the PDSCH transmission cross-carrier-scheduled with PDCCHs of individual cells and uplink HARQ ACK/NACK of the primary cell.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.